The 2005 Nissan Altima exhaust system includes two oxygen sensors. The upstream sensor is located near the exhaust manifold at the front of the exhaust system. The downstream sensor is located near the catalytic converter, further along the exhaust pipe. When a sensor fails, your "Check Engine" light will illuminate. If the "Check Engine" light is on and you notice a decrease in your fuel mileage, an oxygen sensor is the likely problem. Buy a replacement sensor from an auto-parts counter and change it at home in minutes.
Lift the Altima using a jack until it is high enough to fit a set of jack stands under. Rest the car on the jack stands.
Locate the downstream oxygen sensor threaded into the exhaust pipe, approximately halfway down the car, below the center console area. Press the tab on the electrical connection while you pull the connectors apart to disconnect it.
Remove the sensor with a wrench or ratchet fitted with an oxygen sensor socket. Coat the new sensor's threads with anti-seize compound, then hand-thread the sensor into the pipe.
Push the electrical connection together until it clicks. Remove the jack stands by lifting the car slightly with the jack. Lower the Altima to the ground.
